It was the tenth flight for the Challenger (OV-99) and and has as to carry out several lessons from space and observe Halley's Comet.
But that never happened.
73 seconds after launch, the shuttle exploded, killing all seven crew members.
The O-ring seals on one of the Solid Rocket Boosters failed. This caused the booster to pivot and hit the external tank, which is the structure that holds everything together.
This caused the boosters to fly off on their own, as can be seen in the above photo.
The Challenger orbiter rapidly disintegrated due to overwhelming aerodynamic forces.
At least some of the crew survived the explosion, evidence for that is that at least some crew members manually activated their emergency air supplies. But when the cabin crashed into the sea, everyone was killed.
The STS-51-L crew consisted of five NASA astronauts and two payload specialists. From left to right: Ellison Onizuka, Michael J. Smith, Christa Mcauliffe, Dick Scobee, Gregory Jarvis, Ronald McNair, Judith Resnik.
First teacher in space
The Challenger launch was widely watched in schools all across the United States. Approximately 17% of the US population saw it.
The reason for that was Christa McAuliffe, who would be the first teacher in space. This was part of the Teachers In Space Program.
Christa McAuliffe floating in zero G during a preparation flight.
The Challenger Investigation
After the explosion, the Rogers commission, which was tasked with the investigation of the disaster, concluded that the O-rings seals were the cause for failure.
These seals failed because of the unusually cold weather in the night before the launch, temperatures dipped below −3°C (or 27°F). This was well below the minimum temperatures of major components like the Solid Rocket Booster, which was approved up to 4 °C (39 °F)
Icicles on the launch platform indicate the cold
The Aftermath of the Challenger Disaster
Space shuttle launches were suspended for 32 months following the accident.
During that time the Rogers Commission further dug to the root causes of the accident.
They found that NASA's organisational culture and decision making processes had been contributing factors to the accident.
NASA managers had known about the potentials flaw in the design of the O-ring seals as early as 1977 but had failed to act on the information.
Further they ignored warnings from engineers about the danger of launching the morning after such a cold morning.
Only in September of 1988, Space Shuttle Discovery lifted off again for mission STS-26. The boosters had been redesigned and the focus on safety was increased.